<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <button>按钮</button>
    <button>按钮</button>
    <button>按钮</button>
    <button>按钮</button>
    <button>按钮</button>
    <button>按钮</button>
    <script src="js/public.js"></script>
    <script>
        var btn = $$('button')
        for (var i = 0; i < btn.length; i++) {
            btn[i].onclick = function() {
                for (var i = 0; i < btn.length; i++) {
                    btn[i].style.backgroundColor = ''
                }
                this.style.backgroundColor = 'pink'
            }
        }
    </script>
</body>

</html>